1. Technical Field
The present invention relates to a head which ejects a liquid, and a liquid ejecting apparatus which is provided with the head, and particularly relates to an ink jet recording head and an ink jet type recoding apparatus which eject ink as the liquid.
2. Related Art
A piezo ink jet system is an on-demand type ink jet printing system which discharges a liquid droplet by deforming a piezo element through the applying of a voltage to the piezo element (JIS Z8123-1: 2013).
A permanent head is a machine portion or an electrical portion of a printer main body which continuously or intermittently generates a liquid droplet of ink (JIS Z8123-1: 2013).
The permanent head (hereinafter, referred to as a “head”) which is used in the piezo ink jet system is provided with a channel formation substrate on which a pressure generating chamber, which communicates with a nozzle for ejecting a liquid droplet is formed, a piezo element which is provided on one surface side of the channel formation substrate, and a driving circuit board in which a driving circuit, which is bonded onto the channel formation substrate so as to be close to the piezo element and drives the piezo element is provided. The permanent head ejects the liquid droplet from the nozzle by driving the piezo element by the driving circuit and applying a pressure change to the liquid in the pressure generating chamber.
As the piezo element described above, a thin-film type piezo element which is formed on the channel formation substrate through a film formation method and a lithography method has been proposed. When using such a thin-film type piezo element, it is possible to dispose the piezo element at high density; however, it is difficult to electrically connect the piezo element which is disposed at high density and the driving circuit.
For this reason, there have been suggested a configuration such that a bump is provided on the driving circuit board, and the driving circuit and the piezo element are electrically connected to each other via the bump (for example, JP-A-2014-51008).
In this way, by using the bump for connection between the driving circuit and the piezo element, it is possible to easily connect the piezo element which is disposed at high density and the driving circuit at low cost.
However, there is a problem in that if a holding portion, which is a space for accommodating a piezo element, between the driving circuit board and the channel formation substrate is sealed, a pressure change in the holding portion is generated by the driving of the piezo element, and thus the displacement of the piezo element is disturbed due to the pressure change in the holding portion. In addition, if the holding portion is sealed, the pressure of a gas in the holding portion changes due to a temperature change, the displacement of the piezo element is disturbed due to the pressure change in the holding portion, a membrane for separating the holding portion from a flow path is destroyed, ink flows into the holding portion from the flow path, and thereby the piezo element may be destroyed due to the inflowing ink.
In addition, there is a problem in that if the holding portion is sealed, at the time of bonding the driving circuit board and the channel formation substrate, moisture contained in the atmosphere is sealed, and becomes condensation at a low temperature such that the moisture is attached to the piezo element, thereby destroying the piezo element.
Note that such a problem exists in not only a head for ejecting ink, but also a head for ejecting liquid droplets other than the ink.